An electrophotographic light-sensitive material may have various structures depending upon the characteristics required or an electrophotographic process to be employed.
An electrophotographic system in which the light-sensitive material comprises a support having thereon at least one photoconductive layer and, if necessary, an insulating layer on the surface thereof is widely employed. The electrophotographic light-sensitive material comprising a support and at least one photoconductive layer formed thereon is used for the image formation by an ordinary electrophotographic process including electrostatic charging, imagewise exposure, development, and, if desired, transfer.
Furthermore, a process using an electrophotographic light-sensitive material as an offset master plate precursor for direct plate making is widely practiced.
Binders which are used for forming the photoconductive layer of an electrophotographic light-sensitive material are required to be excellent in the film-forming properties by themselves and the capability of dispersing photoconductive powder therein. Also, the photoconductive layer formed using the binder is required to have satisfactory adhesion to a base material or support. Further, the photoconductive layer formed by using the binder is required to have various excellent electrostatic characteristics such as high charging capacity, small dark decay, large light decay, and less fatigue before light-exposure and also have an excellent image forming properties, and the photoconductive layer stably maintains these electrostatic properties to change of humidity at the time of image formation.
Further, extensive studies have been made for lithographic printing plate precursors using an electrophotographic light-sensitive material, and for such a purpose, binder resins for a photoconductive layer which satisfy both the electrostatic characteristics as an electrophotographic light-sensitive material and printing properties as a printing plate precursor are required.
However, conventional binder resins used for electrophotographic light-sensitive materials have various problems particularly in electrostatic characteristics such as a charging property, dark charge retention, a light sensitivity, etc., and smoothness of the photoconductive layer.
Also, the practical evaluations on conventional binder resins which are said to be developed for electrophotographic lithographic master plates have found that they have problems in the above-described electrostatic characteristics, background staining of prints, etc.
In order to overcome the above problems, JP-A-63-217354 and JP-A-1-70761 (the term "JP-A" as used herein means an "unexamined Japanese patent application") disclose improvements in the smoothness of the photoconductive layer and electrostatic characteristics by using, as a binder resin, a resin having a low molecular weight containing from 0.05 to 10% by weight of a copolymer component containing an acidic group in side chains of the polymer or a resin having a low molecular weight (i.e., a weight average molecular weight (Mw) of from 1.times.10.sup.3 to 1.times.10.sup.4) having an acidic group bonded at only one terminal of the polymer main chain thereby obtaining an image having no background stains.
Also, JP-A-1-100554 and JP-A-1-214865 disclose a technique using, as a binder resin, a resin containing a polymer component containing an acidic group in side chains of the copolymer or at the terminal of the polymer main chain, and containing a polymer component having a heat- and/or photo-curable functional groups; JP-A-1-102573 and JP-A-2-874 disclose a technique using a resin containing an acidic group in side chains of the copolymer or at the terminal of the polymer main chain, and a crosslinking agent in combination; JP-A-64-564, JP-A-63-220149, JP-A-63-220148, JP-A-1-280761, JP-A-1-116643 and JP-A-1-169455 disclose a technique using a resin having a low molecular weight (a weight average molecular weight of from 1.times.10.sup.3 to 1.times.10.sup.4) and a resin having a high molecular weight (a weight average molecular weight of 1.times.10.sup.4 or more) in combination; JP-A-1-211766 and JP-A-2-34859 disclose a technique using the above low molecular weight resin and a heat- and/or photo-curable resin in combination; and JP-A-2-53064, JP-A-2-56558 and JP-A-2-103056 disclose a technique using the above low molecular weight resin and a comb-like polymer in combination. The above prior art references disclose that, according to the proposed technique, the film strength of the photoconductive layer can be increased sufficiently and also the mechanical strength of the light-sensitive material can be increased without adversely affecting the above-described electrostatic characteristics by using a resin containing an acidic group in side chains or at the terminal of the polymer main chain.
However, it has been found that, even in the case of using these resins, it is yet insufficient to keep the stable performance in the case of greatly changing the environmental conditions from high-temperature and high-humidity to low-temperature and low-humidity. In particular, in a scanning exposure system using a semiconductor laser beam, the exposure time becomes longer and also there is a restriction on the exposure intensity as compared to a conventional overall simultaneous exposure system using a visible light, and hence a higher performance has been required for the electrostatic characteristics, in particular, the dark charge retention characteristics and photosensitivity.
The present invent-ion has been made for solving the problems of conventional electrophotographic light-sensitive materials as described above and meeting the requirement for the light-sensitive materials.
An object of the present invention is to provide an electrophotographic light-sensitive material having stable and excellent electrostatic characteristics and giving clear good images even when the environmental conditions during the formation of duplicated images are changed to low-temperature and low-humidity or to high-temperature and high-humidity.
Another object of the present invention is to provide a CPC electrophotographic light-sensitive material having excellent electrostatic characteristics and showing less environmental dependency.
A further object of the present invention is to provide an electrophotographic light-sensitive material effective for a scanning exposure system using a semiconductor laser beam.
A still further object of this invention is to provide an electrophotographic lithographic printing plate precursor having excellent electrostatic characteristics (in particular, dark charge retentivity and photosensitivity), capable of reproducing faithful duplicated images to original, forming neither overall background stains nor dotted background stains of prints, and showing excellent printing durability.
Other objects of the present invention will become apparent from the following description and examples.
It has been found that the above described objects of the present invention are accomplished by an electrophotographic light-sensitive material comprising a support having provided thereon a photoconductive layer containing an inorganic photoconductive substance and a binder resin, wherein the binder resin contains an AB block coplymer having a weight average molecular weight of from 1.times.10.sup.3 to 2.times.10.sup.4 and composed of a first block comprising at least one polymer component containing at least one acidic group selected from --PO.sub.3 H.sub.2, --COOH, --SO.sub.3 H, a phenolic hydroxy group, ##STR3## (wherein R represents a hydrocarbon group or -OR' (wherein R' represents a hydrocarbon group)) and a cyclic acid anhydride-containing group, and a second block containing at least a polymer component represented by the following formula (I): ##STR4## wherein R.sub.1 represents a hydrocarbon group.
Furthermore, it has also been found that the mechanical strength (the printing durability in the case of using as a printing plate) of the electrophotographic light-sensitive material can be further improved, when the binder resin used in the present invention contains (i) the above-described AB block copolymer (resin (A)) composed of a component containing the above-described specific acidic group (unless otherwise indicated, the acidic group includes a cyclic acid anhydride-containing group) and a methacrylate component as the block components and (ii) at least one of a heat- and/or photo-curable resin (resin (B)), a crosslinking agent, a resin (C) shown below, a resin (D) shown below, and a resin (E) shown below.
Resin (C)
A resin having a weight average molecular weight of from 5.times.10.sup.4 to 5.times.10.sup.5 and not containing -PO.sub.3 H.sub.2, --COOH, --SO.sub.3 H, phenolic --OH, ##STR5## (wherein R is as defined above), a cyclic acid anhydride-containing group and a basic group.
Resin (D)
A resin having a weight average molecular weight of from 5.times.10.sup.4 to 5.times.10.sup.5 and containing from 0.1 to 15% by weight of a copolymer component containing at least one substituent selected from --OH and a basic group.
Resin (E):
A resin having a weight average molecular weight of from 5.times.10.sup.4 to 5.times.10.sup.5 and containing a copolymer component containing the acidic group at a content of not more than 50% of the content of the acidic group contained in the above-described AB block copolymer (resin (A)), or a resin having a weight average molecular weight of from 5.times.10.sup.4 to 5.times.10.sup.5 and containing a copolymer component containing at least one acidic group which has a pKa higher than the pKa of the acidic group contained in the above-described AB block copolymer (resin (A)) and which is selected from --PO.sub.3 H.sub.2, --SO.sub.3 H, --COOH, and ##STR6## (wherein R represents a hydrocarbon group or --OR.sub.o (wherein R.sub.o represents a hydrocarbon group)).